Denim is cotton cloth which has been dyed, usually blue, with the dye indigo. One desirable characteristic of indigo-dyed denim cloth is the alteration of dyed threads with white threads, which upon normal wear and tear gives denim a white on blue appearance. A popular look for denim is the stonewashed look. Traditionally stonewashing has been performed by laundering the denim material in the presence of pumice stone which results in fabric having a faded or worn appearance with the desired white on blue contrast appearance described above. This stonewashed look primarily consists of removal of dye in a manner to yield a material with areas which are lighter in color, while maintaining the desirable white on blue contrast, and a material which is softer in texture.
Enzymes, particularly cellulases, are currently used in processing denim. In particular cellulases have been used as a replacement for or in combination with pumice stones for the traditional "stonewashing" process used to give denim a faded look. Use of enzymes to stonewash has become increasingly popular because use of stones alone has several disadvantages. For example, stones used in the process cause wear and tear on the machinery, they cause environmental waste problems due to the grit produced and result in high labor costs associated with the manual removal of the stones from pockets of garments. Consequently, reduction or elimination of stones in the wash may be desirable.
Contrary to the use of pumice stones, enzymes (particularly cellulases) are safe for the machine, result in little or no waste problem and drastically reduce labor costs. Therefore, it may be beneficial to use enzymes for stonewashing. However, even though the use of enzymes such as cellulase may be beneficial as compared to stones alone, there are some problems associated with the use of enzymes for this purpose. For example, one problem with some cellulases, such as cellulases from Trichoderma, is what could be described as an incomplete removal of dye caused by "redeposition" or "backstaining" (both terms used interchangeably herein) of some of the dye back onto the fabric during the enzymatic stonewashing process. Such redeposition or backstaining causes blue coloration of the surface, resulting in less contrast between the blue and white threads and abrasion points (i.e., a blue on blue look rather than the preferred white on blue). See American Dyestuff Reporter, September 1990, pp. 24-28.
Redeposition or backstaining is objectionable to some users. Even though Trichoderma cellulases exhibit backstaining, they are preferable to Humicola cellulases, which do not generally exhibit backstaining, because of the higher specific activity on denim material seen with Trichoderma cellulases. In addition, cellulases with a higher degree of purity may be beneficial in the present invention. High specific activity or a high level of purity may result in a higher degree of abrasion in significantly shorter processing times and, therefore, is preferable to the denim processors.
The problem of redeposition of dye during stonewashing has been a concern of denim processors. Previous attempts to address the problem include addition of extra anti-redeposition chemicals, such as surfactants or other agents, into the cellulase wash to help disperse the loosened indigo dye and reduce redeposition. In addition, denim processors have tried using cellulases with less specific activity on denim, along with extra rinsings. This results in additional chemical costs and longer processing times. Another method attempting to address the redeposition problem includes adding a mild bleaching agent or stain removing agent in the process. This method affects the final shade of the garment and increases processing time.
While these methods aid to some limited degree in the reduction of redeposition, the methods are not entirely satisfactory and some objectionable backstaining remains. Use of enzymes and stones together may be advantageous in overcoming this redeposition problem; however, it leaves the processor with some of the problems associated with the use of stones alone.
Based on the shortcomings of previously attempted methods for reducing or preventing redeposition, there is a need for more environmentally favorable and more cost effective methods to address the issue of redeposition or backstaining of dye during stonewash treatment.
Accordingly, it would be desirable to find an enzymatic composition or method that would enhance the removal of the dye during stonewashing when redepositing or backstaining cellulases are used which, although exhibiting backstaining, have a high degree of specific activity on denim material.